PubMed · 9297907
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J Witvoet. 1997. [Should total hip prostheses be cemented?].. https://pubmed.ncbi.nlm.nih.gov/9297907/
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The plane strain fracture toughness of Palacos R bone cement was determined using linear elastic fracture mechanics (LEFM) principles and three different test specimen configurations: single edge notched three-point (SENB), rectangular compact tension (RCT), and chevron notched short rod (CNSR). Another aspect of the study was an investigation of the effect of three methods used to sterilize the powder constituents of the cement-none, gamma irradiation and ethylene oxide--on the fracture toughness of the fully polymerized material. A detailed justification is provided for using LEFM. The fracture toughness results obtained using the CNSR specimens were, on average, 14 and 16% higher than those obtained using the SENB and RCT types, respectively. These differences are accounted for in terms of differences in four aspects of these specimen configuration (namely, residual stress effects, loading rate, material inhomogeneity, and the nature of the test). For a given specimen configuration, gamma irradiation produced a statistically significant decrease in fracture toughness which, it is suggested, is due to the concomitant depreciation in molecular weight. For a given cement type, there is no statistically significant difference in fracture toughness results obtained using SENB and RCT specimens. It is thus suggested that either of these configurations can be used to determine the fracture toughness of acrylic bone cement.
The setting reactions of calcium phosphate cements in the CaHPO4-alpha-Ca3(PO4)2 (DCP-alpha-TCP) system have been investigated. X-ray diffraction (XRD) analyses were performed on DCP-alpha-TCP cement samples of varying calcium to phosphorus (Ca/P) ratios after setting for 24 h in Ringer's solution at 37 degrees C. XRD measurements showed that the intensity of the DCP peaks decreased linearly as the Ca/P ratio of the mixture increased. However, the intensity of the peaks of a new calcium-deficient hydroxyapatite [CDHA; Ca9(HPO4)(PO4)5OH] precipitating phase increased linearly as the Ca/P ratio increased. Alpha-TCP was not detected after 24 h of setting in any sample. A two-phase mixture XRD model was applied to explain the results, and suitable fits were obtained between observed and expected values of the relevant peak heights. The method used for this study also can be applied to studies of the kinetic behavior of other cement systems.
The hardening properties of calcium phosphate cements in the CaHPO4-alpha-Ca3(PO4)2 (DCP-alpha-TCP) system have been investigated with interest focused on the compressive strength and microstructure development. Previous studies have shown that the addition of CaCO3(CC) leads to a modification of the calcium-deficient apatite structure of the reaction product, which results in a material more similar to the apatite in bone mineral. The addition of 10% w/w of CC to the initial DCP-alpha-TCP powder mixture resulted, with time, in a retardation of the development of compressive strength. However, the optimum compressive strength reached values up to 40% higher than CC-free samples. This retarding effect also has been monitored as a function of the calcium to phosphorus (Ca/P) ratio of the DCP and alpha-TCP mixture, showing the importance of the final cement properties of the relative quantities of the reactants in the mixture.